The construction industry is moving towards solvent free construction adhesives to meet volatile organic compound (VOC) regulations currently being enforced in many states, in particular California. Regulations such as Rule 1168 South Coast Air Quality Management will essentially eliminate solvent based adhesives containing 30-40% solvent such as hexane, toluene and acetone. The industry believes that such regulations will be mandated throughout the U.S. and Canada shortly.
In order to meet the various guidelines currently being established by the regulatory organizations, development of a water-based construction adhesive that can meet the VOC requirements while meeting the performance specification of the American Plywood Association (AFG-01) and ASTM C-557 are highly desirable. Solvent based adhesives have in the past set the standards in this area.
Initial attempts at designing a water based adhesive have failed due to performance deficiencies in such areas as strength (moisture resistance) and application characteristics such as "open time".
Some of the difficulties that water based construction adhesives have had in meeting the performance requirements of AFG-01 include the following:
Open time requirements--ranging from 40.degree. F. to 100.degree. F. (5.degree. C. to 38.degree. C.) for 10 minutes.
Freeze-thaw stability--ability to bond to frozen substrates under freezing conditions.
Water-resistance--ability to withstand high humidity in water immersion conditions.
Perhaps the most significant hurdle to overcome in developing a water based construction adhesive is the issue of open time. Typical water based adhesives form a skin when exposed to air, due to the coalescing of the latex particles. At the open time requirements of the industry standard specifications such as 10 minutes at 100.degree. F. (38.degree. C.), water based adhesives form an irreversible skin before the bond is made which causes poor adhesion to the substrate. Solvent based systems do not suffer from this deficiency because, after a skin is formed and a bond is made, the solvents in the adhesive will redisperse the rubber phase and cause wetting of the substrate, thus achieving a durable bond.